The use of a contingent valuation (CV) method is controversial among economists because it is based on hypothetical rather than real economic choices. This paper reports the results of an experiment designed to elicit the real and the hypothetical willingness to pay (WTP) for a private good. The effect of different settings of knowledge (direct and indirect) of the good on subjects' valuation behaviour are investigated. The findings show that (i) a direct knowledge of the good reduces the observed disparity between hypothetical and real WTP; and that (ii) different settings of knowledge generate different perceptions of the characteristics of the good.